There are multiple approaches to transfer files to or from a Compute Engine instance in GCP. Here are some popular methods:

1. Using SCP (Secure Copy Protocol):

SCP is a popular method for transferring files securely over SSH.

Transfer files to the instance:

gcloud compute scp LOCAL_FILE_PATH INSTANCE_NAME:REMOTE_FILE_PATH --zone ZONE

Transfer files from the instance:

gcloud compute scp INSTANCE_NAME:REMOTE_FILE_PATH LOCAL_FILE_PATH --zone ZONE

Replace LOCAL_FILE_PATH, REMOTE_FILE_PATH, INSTANCE_NAME, and ZONE with appropriate values.

2. Using SFTP (Secure File Transfer Protocol):

SFTP is a secure way to transfer files over an SSH connection.

a. Install an SFTP client (such as FileZilla, WinSCP, or Cyberduck) on your local machine.

b. Obtain the external IP address of your Compute Engine instance from the GCP Console or by running gcloud compute instances describe INSTANCE_NAME --zone ZONE --format="get(networkInterfaces[0].accessConfigs[0].natIP)".

c. Configure the SFTP client with the following settings:

• Host: The external IP address of your instance
• Port: 22
• Protocol: SFTP
• Username: Your instance username (default is your Google Cloud account email prefix)
• Password/Key: Your private SSH key file (usually located in ~/.ssh/google_compute_engine)

d. Connect to the instance and transfer files using the SFTP client’s interface.

3. Using Google Cloud Storage:

You can transfer files between your local machine and the Compute Engine instance using Google Cloud Storage.

a. Install the gsutil tool on your local machine by following the instructions at https://cloud.google.com/storage/docs/gsutil_install.

b. Create a Cloud Storage bucket using the GCP Console, gsutil, or Terraform.

Transfer files to the instance:

• Upload files to the Cloud Storage bucket:

gsutil cp LOCAL_FILE_PATH gs://BUCKET_NAME/REMOTE_FILE_PATH

• SSH into the instance and download files from the bucket:

gcloud compute ssh INSTANCE_NAME --zone ZONE
gsutil cp gs://BUCKET_NAME/REMOTE_FILE_PATH LOCAL_FILE_PATH

Transfer files from the instance:

• SSH into the instance and upload files to the Cloud Storage bucket:

gcloud compute ssh INSTANCE_NAME --zone ZONE
gsutil cp LOCAL_FILE_PATH gs://BUCKET_NAME/REMOTE_FILE_PATH

• Download files from the bucket to your local machine:

gsutil cp gs://BUCKET_NAME/REMOTE_FILE_PATH LOCAL_FILE_PATH

Replace LOCAL_FILE_PATH, REMOTE_FILE_PATH, INSTANCE_NAME, ZONE, and BUCKET_NAME with appropriate values.

These are some of the popular methods for transferring files to and from a Compute Engine instance in GCP. Note that Terraform is not directly used for file transfers but can help create resources like a Google Cloud Storage bucket.